1. Technical Field
The invention relates to ballistic resistant materials and articles formed from fiber plies that incorporate multiple different fiber types within a single fiber ply.
2. Description of the Related Art
Ballistic resistant articles containing high strength fibers are well known. Articles such as ballistic resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high strength fibers. Many types of high strength fibers are known, such as ultra-high molecular weight polyethylene fibers, aramid fibers, polybenzoxazole fibers, liquid crystal copolyester fibers and M5® rigid rod fibers. See, for example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, the disclosures of which are incorporated herein by reference to the extent consistent herein, which describe ballistic resistant composites formed from ultra-high molecular weight polyethylene.
Each fiber type has its own unique characteristics and properties, and as a result, the properties of composites fabricated from high strength fibers may vary depending on fiber type used. For example, aramid fibers have high surface energy because their surfaces contain polar functional groups, and thus resins generally exhibit a strong affinity for aramid fibers. In comparison, ultra-high molecular weight polyethylene fibers are naturally inert and generally exhibit a weaker affinity for resin coatings. This difference can be important depending on the desired end use of the composite.
Another factor affecting ballistic resistance is the type of fabric construction. For example, in applications such as bullet resistant vests, it may be desirable to fabricate woven or knitted fabrics without coating the fibers with a polymeric binder to form flexible fabric composites. In other applications, such as bullet resistant helmets, it may be desirable to encapsulate or embed fibers in a polymeric binder material to form non-woven, rigid fabric composites.
In this regard, non-woven, unidirectional composites are among the highest performing materials in the armor industry. In a typical method for manufacturing non-woven, unidirectional composites, multiple plies of unidirectionally arranged fibers are stacked orientation and pressed together with heat and pressure to produce a composite. To take advantage of the different properties of different fiber types, it has been known to form hybrid, non-woven composites where fiber plies formed from differing fiber types are combined into a single armor structure. See, for example, U.S. Pat. Nos. 5,179,244 and 5,180,880 which teach body armor where aramid and non-aramid fiber plies are joined into a combined structure. See also U.S. Pat. No. 6,119,575 which teaches a hybrid structure comprising at least one ply of aromatic fibers in a first polymeric matrix, at least one ply of a woven plastic, and at least one ply of polyolefin fibers in a second polymeric matrix.
In each of the composites described in U.S. Pat. Nos. 5,179,244; 5,180,880 and 6,119,575, each of the individual component plies consists of only one fiber type, where one unidirectional fiber ply is composed of all one fiber type and other fiber plies are composed of another fiber type. Such a construction fails to take full advantage of the differing properties of the different fibers, such as resin adhesion, consolidation temperature, frictional characteristics, cut resistance, etc. Additionally, due to the nature of their physical construction, such hybrid structures are unduly limited in composite homogeneity and in the percentage of each fiber type within a composite. There is a need in the art for a solution to these drawbacks, and this invention provides a solution to this need. Particularly, it has been found that by combining different types of fibers within a single fiber ply, a synergistic effect is achieved wherein the varied properties of each fiber type better complement each other to thereby form an improved ballistic resistant composite.
The ballistic penetration resistance of a composite is directly related to the strength of the constituent fibers of the composite, where increases in fiber strength properties such as tenacity and/or tensile modulus correlate with an increase in V50 velocity. Accordingly, fibers having high tensile properties, such as ultra-high molecular weight polyethylene fibers, are desirable herein. There is also a direct correlation between backface signature (also known in the art as “backface deformation”, “trauma signature” or “blunt force trauma”) and the bond strength of a resin coating on a fiber at the resin/fiber interface, where stronger bond strength correlates with lower backface signature. Accordingly, fibers having a strong affinity for resin/polymer coatings, such as aramid fibers, are desirable herein.
Other high performance structural fibers, such as carbon fibers, glass fibers, and polyester fibers, such as polyethylene terephthalate and polyethylene naphthalate fibers, are known to provide other desirable properties such as thermal stability, abrasion resistance, cut resistance and impact energy absorption. The fibrous materials of the invention are formed from one or more hybrid fiber plies that are formed by combining at least two different fiber types to take advantage of the different advantageous properties provided by each fiber type without trading off or sacrificing other desired properties.